The present invention relates to a method for nondestructively inspecting the joint portion of members being welded by friction stir welding and the like, and the present nondestructive inspection is especially preferably applied to inspecting friction-stir-welded areas of aluminum alloy members used for example to construct railway cars and buildings.
Friction stir welding is a method performed by inserting a rotating round shaft (called a rotary tool) to the members to be welded and moving the same along the joint line, thereby heating, softening, plasticizing and solid-phase welding the joint portion. The rotary tool comprises a large-diameter portion and a small-diameter portion. Upon welding, the small-diameter portion is inserted to the members, and the end surface of the large-diameter portion comes into contact with the welded members. A projection is provided to the joint portion in advance, which functions as the filler material for filling the gap that may exist between the two members. The central axis of the rotary tool is somewhat tilted. A cutting blade can be equipped to the large-diameter portion of the rotary tool for welding and cutting the projections simultaneously. Air is blown to remove the swarf from the upper surface of the projection. This method is disclosed in Japanese Patent Laid-Open Publication No. 2001-47262 (EP 1057575 A2).
When members are welded by an ordinary welding method, a void may be created at the joint region. However, since this void is generally spherical, it does not seriously affect the strength of the welded portion.
In case of friction stir welding, however, the defect is not spherical. If defect occurs, it is often continuous. In such case, it seriously defects the strength of the welded members.
In general, a nondestructive inspection is performed by manually sliding a probe generating ultrasonic wave along the joint portion, which requires much experience and skill.
Moreover, weld flash is formed on both sides of the weld portion by the friction stir welding. A semicircular pattern is created on the surface of the joint portion, which also causes flash. Therefore, it is difficult to inspect the welded members from the surface of the joint region. Even further, a semicircular recess or groove is formed on the surface of the joint region, which also makes inspection difficult.
Therefore, after completing the friction stir welding, it is possible to remove the flash and other unevenness by a separate cutting process and the like, and then perform the inspection. However, such method takes time and is costly.
The first object of the present invention is to automate the nondestructive inspection procedure of the friction stir welding portion.
The second object of the present invention is to reduce the cost for inspecting the welding portion.
The first object of the present invention is achieved by relatively moving a rotary tool against the members to be welded and friction stir welding said members, cutting a part of the welded portion at the same time, and performing a nondestructive inspection at a rear position therefrom.
The second object of the present invention is achieved by cutting a part of the welded portion and performing a nondestructive inspection at a rear position therefrom.